Reversing a vehicle while towing a trailer can be challenging for many drivers, particularly for drivers that drive with a trailer on an infrequent basis or with various types of trailers. Systems used to assist a driver with backing a trailer frequently estimate the position of the trailer relative to the vehicle with a sensor that determines a steering input for the vehicle based on an input trailer curvature path and determined a hitch angle. Both the hitch angle determination and the steering input determination require use of a kinematic model of the combined trailer and vehicle that includes both the length of the trailer, more particularly, from the point of attachment with the vehicle to the front axle thereof and an angle between the vehicle and the trailer at that point of attachment. While some systems have relied on user input for the trailer length, doing so may place an undesired burden on the user and may introduce inaccuracies that some such systems are unequipped to handle. The accuracy and reliability of the calculations involving trailer length can be critical to the operation of the backup assist system. Accuracy of the trailer-vehicle angle (also referred to as the “hitch angle”) is similarly important in determining the kinematic relationship. Accordingly, improvements related to automated system estimation of trailer length and hitch angle in an accurate manner may be desired.